Method and system for ladar pulse deconfliction

ABSTRACT

Disclosed herein are a number of example embodiments that employ controllable delays between successive ladar pulses in order to discriminate between “own” ladar pulse reflections and “interfering” ladar pulses reflections by a receiver. Example embodiments include designs where a sparse delay sum circuit is used at the receiver and where a funnel filter is used at the receiver. Also, disclosed are techniques for selecting codes to use for the controllable delays as well as techniques for identifying and tracking interfering ladar pulses and their corresponding delay codes. The use of a ladar system with pulse deconfliction is also disclosed as part of an optical data communication system.

CROSS-REFERENCE AND PRIORITY CLAIM TO RELATED PATENT APPLICATIONS

This patent application is a continuation of U.S. patent applicationSer. No. 15/896,262, filed Feb. 14, 2018, and entitled “Method andSystem for Optical Data Communication via Scanning Ladar”, now U.S. Pat.No. 11,092,676, which claims priority to provisional U.S. patentapplication Ser. No. 62/460,520, filed Feb. 17, 2017, and entitled“Method and System for Ladar Pulse Deconfliction”, the entiredisclosures of which are incorporated herein by reference.

This patent application is related to (1) U.S. patent application Ser.No. 15/896,219, filed Feb. 14, 2018, and entitled “Ladar PulseDeconfliction Method”, now U.S. Pat. No. 10,379,205, (2) U.S. patentapplication Ser. No. 15/896,233, filed Feb. 14, 2018, and entitled“Ladar Pulse Deconfliction Apparatus”, now U.S. Pat. No. 10,386,467, (3)U.S. patent application Ser. No. 15/896,241, filed Feb. 14, 2018, andentitled “Method and System for Ladar Pulse Deconfliction Using DelayCode Selection”, now U.S. Pat. No. 10,185,028, and (4) U.S. patentapplication Ser. No. 15/896,254, filed Feb. 14, 2018, and entitled“Method and System for Ladar Pulse Deconfliction to Detect and TrackOther Ladar Systems”, now U.S. Pat. No. 10,209,349, the entiredisclosures of each of which are incorporated herein by reference.

INTRODUCTION

It is believed that there are great needs in the art for improvedcomputer vision technology, particularly in an area such as automobilecomputer vision. However, these needs are not limited to the automobilecomputer vision market as the desire for improved computer visiontechnology is ubiquitous across a wide variety of fields, including butnot limited to autonomous platform vision (e.g., autonomous vehicles forair, land (including underground), water (including underwater), andspace, such as autonomous land-based vehicles, autonomous aerialvehicles, etc.), surveillance (e.g., border security, aerial dronemonitoring, etc.), mapping (e.g., mapping of sub-surface tunnels,mapping via aerial drones, etc.), target recognition applications,remote sensing, safety alerting (e.g., for drivers), and the like.

As used herein, the term “ladar” refers to and encompasses any of laserradar, laser detection and ranging, and light detection and ranging(“lidar”). Ladar is a technology widely used in connection with computervision. In an exemplary ladar system, a transmitter that includes alaser source transmits a laser output such as a ladar pulse into anearby environment. Then, a ladar receiver will receive a reflection ofthis laser output from an object in the nearby environment, and theladar receiver will process the received reflection to determine adistance to such an object (range information). Based on this rangeinformation, a clearer understanding of the environment's geometry canbe obtained by a host processor wishing to compute things such as pathplanning in obstacle avoidance scenarios, way point determination, etc.

However, as ladar usage grows, particularly in fields such as automobilevision, the global presence of millions and potentially billions ofladar systems in the field poses a daunting technical challenge: how canthe ladar systems be designed to differentiate their own ladar returnsfrom those of other ladar systems? For example, it can be expected inautomobile use cases that traffic patterns will often involve many ladarsystems transmitting ladar pulses in close proximity to each other. Thiswill result in a ladar receiver of a given ladar system receiving alight signal that may include not only the ladar pulse reflection fromthat ladar system's ladar transmitter (its “own” pulse), but also ladarpulses and ladar reflections from the ladar transmitters of other ladarsystems (“interfering” pulses). Thus, it should be understood that ladarreceivers will detect noisy light signals, and there is a need fortechnology that is capable of distinguishing between “own” pulsereflections and “interfering” pulses/pulse reflections within this noisysignal while operating in real-time in the field.

As a solution to this technical challenge, the inventors disclose thatthe ladar transmitters can be designed to encode their own ladar pulsesvia a delay between successive ladar pulses. Thus, different ladartransmitters can employ different delays between successive ladar pulsesto allow ladar receivers to distinguish between “own” ladar pulses and“interfering” ladar pulses. Preferably, these delays are fairly shorttime intervals and the number of pulses in the pulse sequence is keptlow so as to keep the square root loss in effective energy low.Accordingly, the encoding can be referred to as a sparse burst code. Forexample, in an example embodiment, the pulse sequence can be a pulsepair (doublet) such that a single delay between pulses is used todistinguish “own” pulses from “interfering” pulses. In another exampleembodiment, the pulse sequence can be three pulses (triplet) such thattwo delays are used for encoding. In general, it should be understoodthat for a sequence of n pulses (n-tuple), there would be n−1 delaysthat can be used for encoding. Another benefit of the sparse burst codeis that the number of samples needed to represent the pulses can be low,which contributes to computational efficiency and low latencyprocessing.

Also, in various example embodiments, the ladar receiver system candecode the received delay-encoded pulses without the need forcooperation or communication with outside systems which is advantageousin situations where such communication may not always be possible oravailable. Further still, the pulse decoding process for thedelay-encoded pulses can be efficiently implemented by the receiversystem such that the ladar system can still operate at desired speeds.

A delay sum circuit can be employed to detect the presence of “own”pulse reflections within a received ladar signal. In an exampleembodiment, the delay sum circuit can perform coarse-grained pulsedetection. In another example embodiment, the delay sum circuit can beaugmented with additional comparators to perform fine-grained pulsedetection.

A variety of techniques are described herein that can be used to selectthe delays used by a universe of ladar systems so as to reduce thelikelihood of undesired pulse collisions where two ladar systems employthe same delays between pulses.

The inventors also disclose that the pulse deconfliction techniquesdescribed herein can also be used to detect and track the existence ofother ladar systems in an environment that employ different delay codesbetween ladar pulses.

Further still, the inventors disclose various optical data communicationtechniques that leverage the scanning ladar system to send and receivemessage data via encoded ladar pulses. Furthermore, laser dosagetracking as described herein can be employed to reduce the risks ofoverly exposing humans and cameras to excessive laser light.

These and other features and advantages of the present invention will bedescribed hereinafter to those having ordinary skill in the art.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 discloses an example environment where multiple ladar systems maypose interference threats to each other.

FIG. 2A depicts an example signal processing circuit that can be usedfor doublet pulse deconfliction to decode an incoming signal and detectthe presence of any “own” pulse reflections using sparse summation.

FIG. 2B shows another example embodiment of a signal processing circuitthat can be used for doublet pulse deconfliction using sparse summationwith data adaptive thresholding.

FIG. 2C shows an example embodiment of a signal processing circuit thatcan be used for triplet pulse deconfliction using sparse summation.

FIG. 2D shows an example process flow for enhanced deconfliction using atriple comparator, which can be applied to delay code(s) of any length.

FIG. 3A depicts an example signal processing circuit that can be usedfor doublet pulse deconfliction to decode an incoming signal and detectthe presence of any “own” pulse reflections using the triple comparatorscheme in 2D for fine-grained detection.

FIG. 3B shows another example embodiment of a signal processing circuitthat can be used for fine-grained doublet pulse deconfliction. Thisembodiment expands on FIG. 3A by adding a data adaptive threshold.Because of the shape of the decision region we call this a funnelfilter.

FIG. 3C shows formulas that can be used to measure various detectionmetrics.

FIG. 4 shows a plot that measured filter performance in terms ofdetection probability versus SNR for doublets and triplets.

FIG. 5 shows an example process flow for generating delay codes usinghashing techniques.

FIGS. 6A and 6B show an example performance model for vehicle usagescenarios.

FIG. 7 shows an example process flow for using position detection toinfluence delay code selection.

FIG. 8 shows an example process flow for using vehicle-to-vehiclecommunications to collaboratively define delay codes.

FIG. 9 shows an example process flow for using billboard techniques todefine delay codes.

FIG. 10 shows an example pulse deconfliction data flow for a case of 8bits, 800 MHz ADC, with a triple pulse code, with maximum code delaylength of 80 nsec.

FIG. 11 shows various options for code assignment/re-assignment incombination with online transmit/receive/detect operations.

FIG. 12 shows an example embodiment of a ladar receiver augmented toalso receive other optical information.

FIG. 13 shows an example embodiment of an optical transceiver that canserve as a free space, point-to-point optical data communication system.

FIGS. 14A and 14B show example embodiments of a laser heat map controlloop.

DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS

FIG. 1 depicts an example environment where there are multiple ladarsystems 100 (e.g., 100 ₁, 100 ₂, . . . 100 _(n)) that transmit ladarpulses. Each ladar system 100 comprises a ladar transmitter 102, a ladarreceiver 104, and a control system 106. Each ladar transmitter 102 isconfigured to generate and transmit ladar pulses into the environment.Each ladar receiver 104 is configured to receive and detect a lightsignal that may include ladar pulse reflections. As noted above, thisreceived signal may also include noise such as interfering pulses/pulsereflections from other ladar systems. Each control system 106 can beconfigured to control how its corresponding ladar transmitter 102 andladar receiver 104 operate. Examples of suitable ladar systems 100 aredisclosed and described in greater detail in U.S. patent applicationSer. No. 62/038,065, filed Aug. 15, 2014; and U.S. Pat. App. Pubs.2016/0047895, 2016/0047896, 2016/0047897, 2016/0047898, 2016/0047899,2016/0047903, 2016/0047900, 2017/0242102, 2017/0242103, 2017/0242104,2017/0242105, 2017/0242106, 2017/0242107, and 2017/0242109, the entiredisclosures of which are incorporated herein by reference. For example,the ladar system 100 may employ a ladar transmitter 102 (as described inthe above-referenced and incorporated patent applications) that includesscanning mirrors and uses a range point down selection algorithm tosupport pre-scan compression (which can be referred herein to as“compressive sensing”). Such an embodiment may also include anenvironmental sensing system 120 that provides environmental scene datato the ladar transmitter to support the range point down selection.Through the use of pre-scan compression, such a ladar transmitter canbetter manage bandwidth through intelligent range point targetselection. Furthermore, because the detection and image quality for aladar system varies as the square root of the number of pulses used perpoint cloud, this means that reducing the required number ofcommunication pulses via the compressive sensing enhances the signal tonoise ratio (SNR), enabling robust pulse collision avoidance withoutgreatly reducing detection range or position accuracy. Accordingly, thepulse deconfliction techniques described herein are particularlybeneficial when combined with a ladar transmitter that employscompressive sensing. While these referenced and incorporated patentapplications describe example embodiments for ladar systems 100, itshould nevertheless be understood that practitioners may choose toimplement the ladar systems 100 differently than as disclosed in thesereferenced and incorporated patent applications.

The ladar systems can distinguish between each other's pulses based onthe delays that are present between successive ladar pulses transmittedby each ladar transmitter 102. Thus, the ladar transmitter 102 for ladarsystem 100 ₁ can generate a pulse sequence 110 ₁ with a delay of Lbetween pulses 112 ₁ and 114 ₁. The ladar transmitter 102 for ladarsystem 100 ₂ can generate a pulse sequence 110 ₂ with a delay of Mbetween pulses 112 ₂ and 114 ₂, and so on (including ladar transmitter102 for ladar system 100 _(n) generating a pulse sequence 110 _(n) witha delay of N between pulses 112 _(n) and 114 _(n)). It should beunderstood that L, M, and N are all different values to support pulsedifferentiation by the ladar systems 100. Also, while the example ofFIG. 1 shows that the various pulse sequences 110 are doublets, itshould be understood that longer pulse sequences could be used ifdesired by a practitioner (e.g., a n-tuple pulse sequence where eachpulse sequence includes n−1 delays).

FIG. 2A depicts an example signal processing circuit 220 that can beused on the ladar system 100's receive side to decode an incoming signalto detect the presence of any “own” pulse reflections. The “own” ladarpulse transmitted by the subject ladar system 100 can be expected tolargely retain the delay L between its pulses when it strikes an objectin the environment and is reflected back to the receiver 104. However,as indicated above, the signal sensed by receiver 104 will also includenoise such as interfering ladar pulses and interfering pulsereflections. For ease of illustration, FIG. 2A shows the presence ofboth an “own” ladar pulse reflection 210 and an “interfering” ladarpulse reflection 280, each with its own delay between pulses (where the“own” ladar pulse reflection 210 includes a delay of L between pulses212 and 214 while the “interfering” ladar pulse reflection 280 includesa delay of M between pulses 282 and 284).

The signal processing circuit 220 can be referred to as a “sparse delaysum circuit”. The signal processing circuit 220 provides coarsefiltration while simultaneously creating pulse collision excision andrecombining n-tuples (e.g., doublets) for subsequent point cloudformation. This arrangement allows for in-stride collision removal andhelps support an inspection of every single sample of the signal sensedby the receiver's photodetector for an arbitrary number of interferingladar systems (e.g., other vehicles) in view of the “own” ladar system.Only n−1 delays are needed to uniquely determine an n-tuple code. Thesignal processing circuit 220 does not rely on intensity or individualpulse shape and is hence robust to attenuation and pulse spreading.

The summation indicated by 216 in FIG. 2A represents the effect ofphysics and occurs “in the air” as the electromagnetic waves from theincoming ladar pulse reflections 210 and 280 commingle with each other.Thus, the light 218 sensed by receiver 104 is a commingling of ladarpulse reflections 210 and 280 as well as other sources of light noise.Receiver 104 includes a light sensor such as a photodetector. Receiver104 may also include features such as an optical front end and ananalog-to-digital converter (ADC), although this need not be the case.An example embodiment of suitable receiver technology for use asreceiver 104 is described in the above-referenced and incorporated U.S.Pat. App. Pub. 2017/0242105. The receiver 104 will thus sense incominglight 218 and generate a signal representative of the sensed light(which includes signal portions attributable to “own” ladar pulsereflection 210 and the interfering ladar pulse reflection 280). In anexample embodiment where the receiver 104 includes an ADC, the sensedlight signal produced within the receiver can be represented by aplurality of digital samples.

In the example embodiment of FIG. 2A, these samples are passed into twochannels 222 and 224. Channel 222 includes a delay circuit 226 that isconfigured to impose a delay of L on the samples, where L is the valueknown by the system as the delay code for an “own” ladar pulse. Theoutput of the delay circuit 226 will be a signal 228 that is a delayedversion (by L samples) of the signal entering channel 222. The delaycircuit 226 can be embodied in any form suitable for delaying the signalcoming into channel 222 by L, whether in hardware, firmware, software,combinations thereof or achieved electronically, optically,acoustically, and/or magnetically. In a digital embodiment where thetime delay L between pulses can be represented by a count of samples, Lcan be the number of samples that would represent the time delay betweenpulses 212 and 214.

Channel 224 passes the unaltered samples from the receiver 104 to addercircuit 230. Adder circuit adds the delayed signal 228 with theundelayed signal in channel 224. Signal 232 that is output by addercircuit 230 thus represents the summation of the undelayed signal fromthe receiver and its delayed counterpart. In the absence of any noisewithin the signal from the receiver, it should be understood that theadder output signal 232 will exhibit a peak value when the second pulse214 of the “own” ladar pulse reflection 210 is received and processed bythe signal processing circuit 220. Accordingly, this peak would identifywhen a valid “own” pulse reflection is received. However, the presenceof noise within the signals will tend to obscure such peaks.

To provide a coarse filter for detecting own ladar pulse reflectionswithin the noise-impacted signal from the receiver, comparator circuit234 can be used. Comparator 234 compares the adder output signal 232with a value T. If signal 232 is greater than T, the signal can bedeemed as likely including the “own” pulse reflection 210. If the signal232 is less than T, the signal can be deemed as likely not including the“own” pulse reflection 210. The value of T can be a statisticalcharacterization of a floor above which the signal would likely containthe “own” pulse reflection 210 (derived from the observation above thatsignal 232 will tend to exhibit peak values when the “own” pulsereflection is present). The value of T can be fed into comparator 234from a register 236. The output of comparator 234 can be a signal 238that is indicative of whether the signal from the receiver likelyincludes the “own” pulse reflection 210. By way of example, this signal238 could be a binary yes/no flag to that effect.

FIG. 2B depicts an example embodiment of signal processing circuit 220where the circuit 220 includes T compute logic 250. This compute logic250 can be configured to compute a value for T based on the signal fromthe receiver. Accordingly, as the characteristics of the received signalchange, the value for T may adaptively change. This feature is usefulwhen the noise “floor” is comprised of ambient light (e.g., duringdaytime), other ladar light, and/or other external sources. When thesystem is known to be limited by a noise floor that is mere thermalnoise, the nonadaptive threshold in FIG. 2A is preferred. Compute logic250 can compute a moving average of the samples output from the receiverand passing into channels 222 and 224. This can be a running averagewith any chosen sliding window size. A subset of the samples can be used(trickle moving average) to cut down on computations:

-   -   1) Take the summation of the squares of the past J samples.    -   2) If any past samples have been declared “valid” pulses, remove        these D terms from the sum.    -   3) Divide this summation by the number of samples remaining in        the sum after subtraction and denote the result by Q.    -   4) Set T=α/√{square root over (Q)}, where α is the desired        number of standard deviations.

While FIGS. 2A and 2B show examples where the pulse coding uses onedelay (a doublet pulse), it should be understood that if the pulsecoding uses multiple delays, the signal processing circuit 220 canaccommodate this through additional taps in the delay line and cascadedadders. Such an approach can be referred to as a “cascaded sparse delaysum circuit”.

For example, FIG. 2C shows an example embodiment where the “own” ladarpulse is a triplet pulse 290 that includes two delays, L₁ between pulses292 and 294 and L₂ between pulses 294 and 296. With this arrangement,channel 222 includes two delay circuits 226 and 270. Delay circuit 226can operate as described above in connection with FIG. 2A to impose adelay of L₁ on the incoming samples. Delay circuit 270 then operates todelay the delayed signal 228 with a delay of L₂ to create anotherdelayed signal 272 that delays the incoming samples at 222 by L₁ and L₂.

The cascaded adders comprise an adder 230 that taps into delayed signal228 to sum delayed signal 228 with the undelayed signal in channel 224,where the output 232 from adder 230 is fed into a downstream addercircuit 274 that taps into delayed signal 272 for summing with adderoutput signal 232 to yield adder output signal 276.

Comparator 234 then compares adder output signal 276 with T to generatesignal 238 as discussed above. As explained in connection with FIG. 2B,the value of T can be computed using T compute logic 250 (as shown byFIG. 2B) based on the signal from the receiver.

The triplet pulse encoding involved in FIG. 2B also helps solve achallenge during operation that may arise as a result of multipathdiffusion from interfering ladar pulses/pulse reflections. To mitigatethis challenge, the extra pulse and delay in the triplet yields a thirdcode index that forms a triplet sparse aperture code, reducing the riskof falsely accepting a spurious pulse in the (unlikely but possible)event that the received spurious signal matched a two-pulse codeconfiguration. The triplet sparse aperture code also mitigates clockjitter-induced spurious pulse collisions. For example, suppose thetriplet code delays for the “own” ladar pulse are 3,19 (which yields asignal in the form of y(k), y(k−3), and y(k−19)). Now further supposethat the spurious, interfering pulse presents a return over the range[y(k),y(k−3)]. In this situation, a doublet detector may declare thecode valid, which constitutes a false positive. By adding a third term,the odds of triggering [exceeding the threshold T] in the triple sum(vice double sum) from a single bounce path is very low. Furthermore, athree-pulse [triplet] code presents the practitioner with

$\frac{n\left( {n - 1} \right)}{2} \approx \frac{n^{2}}{2}$codes (where n is the maximum delay). So, for an example where n=60,this provides about 12 bits of isolation. Therefore, a triplet codeenhances isolation against interfering ladars.

While the circuit FIG. 2C operates effectively, the inventors expectthat even better performance can be obtained by using a funnel filterapproach as described herein. Such an approach is expected to mitigateboth multipath diffusion and pulse collisions from interfering ladars,for doublet, triplet, or any n-tuple code. FIG. 2D shows an exampleprocess flow for the logic flow of the funnel filter. We use N_(tuple)to denote code length for clarity. We first screen by using the simplesum and threshold process of FIGS. 2B,2C (or the extension toN_(tuple)>2, to screen for candidate codes). Consider the doublet caseand denote these two samples as x,y, with x the largest of the two. Weaccept the candidate code when the following three conditions aresatisfied, for some fixed τ>1:

-   -   1) x+y>T    -   2) x<τy    -   3) y<τx        Note that 2),3) combined is the same as computing max(x/y,y/x)<τ        (see discussion below relating to a triple comparator approach).

Therefore the above three steps align with FIG. 2D, with 1) beingscreening in FIG. 2D, and probing/rejection in FIG. 2D being implementedby 2),3). The reason we choose not to explicitly form the maximum isbecause it is faster to evaluate 2),3). For a doublet pulse it is alsoeasier to find the detection statistics, as described in FIG. 4 .However, it should be noted that, for more than two pulses, we canexplicitly form a maximum and minimum. The probe step 1), is the sparsesum from FIGS. 2B,2C. Clearly, more energy is an indicator of valid codepresence. As to the value of T to be chosen, suppose the presence of acode returns a value S+N_(oise), and noise only returns a value ofN_(oise). Then we should pick a value of T so thatS+N_(oise)>T>N_(oise). Further the choice of T in this interval willallow us to trade false alarms and detection probability as discussed inFIG. 4 .

Step 2),3) are motivated and justified as follows. Suppose we had nonoise and so x=y=S. Then a value of τ=1 allows a true pulse to pass, butany noise will cause the filter to reject that sample. So, as we make τlarger, we increase the detection probability when noise is present atthe expense of more false alarms. Using the same argument, we see thatthe other threshold T should be chosen so that N_(oise)<T<2S.

FIG. 3A shows a signal processing circuit 300 that includes signalprocessing circuit 220 of FIG. 2A [which can perform step 1) from above]with additional filtration circuitry, mainly the probe stage [which canperform steps 2),3) from above], which can take the form of two morecomparisons. Note that in the triple comparator, one comparison is withthe threshold T and the other two with τ. With the augmentation of FIG.3A, the own pulse detection is now based on a triple comparator. Thetriple comparator arrangement provides a nonlinear decision region whichprovides more fine-grained preservation of valid “own” ladar pulsereflections while rejecting interfering pulses/pulse reflections.Comparator 234 operates as described above in connection with FIG. 2A.However, multiplier 302 taps into the signal in channel 224 andmultiplies this signal by the value τ to produce a first product signal308. Also, multiplier 304 taps into the delayed signal 222 andmultiplies this delayed signal by τ to produce a second product signal310. The value of τ can be fed into multipliers 302 and 304 from aregister 306.

Comparator 312 compares the delayed signal 228 with the first productsignal 308. If the delayed signal 228 is less than the first productsignal 308, this indicates that the two pulses x,y differ substantially,and the output signal 316 from comparator 312 can indicate that it isdeemed unlikely that the own ladar pulse reflection 210 is present inthe signal.

Comparator 314 compares the undelayed signal in channel 224 with thesecond product signal 310. If the undelayed signal at 224 exceeds thesecond product signal 310, this again indicates that x,y differsignificantly, which cannot occur for a valid pulse present on bothchannels, and the output signal 318 from comparator 314 can indicatethat it is deemed unlikely that the own ladar pulse reflection 210 ispresent in the signal.

The circuit 300 can also include AND logic 320 downstream fromcomparators 234, 312, and 314. AND logic 320 will operate to go highwhen all of the outputs 238, 316, and 318 from comparators 234, 312, and314 are high. A high (yes) signal at AND output 322 will indicate thatthe fine-grained filter has detected the presence of the “own” ladarpulse reflection within the signal. A signal that passes the testsimposed by the three comparators 234, 312, and 314 will enjoy twoattributes, namely (1) the sum of candidate pulse pairs will be large(by virtue of the decision by comparator 234), and (2) the inter-pulsedeviation will be small. If any of the outputs 238, 316, and 318 fromcomparators 234, 312, and 314 are low, the output signal 322 from ANDlogic 320 will indicate that the “own” ladar pulse reflection is notpresent within the signal from the receiver.

FIG. 3A also shows a selector circuit 324 that uses signal 322 toclassify a sliding window of the signal samples as either an “own” pulsereflection 326 or noise/interference 328. Samples classified as an “own”pulse reflection 326 by signal 322 can be further processed to extractrange information while samples classified as noise/interference 328 bysignal 322 can be dropped into a bit bucket 330 and/or otherwiseprocessed to gain additional information about the noise/interference.

The triple comparator filter of FIG. 3A can be implemented using only afew logic gates, additions, and multiplications which makes it amenableto low latency pulse detection. Furthermore, it should be understoodthat a practitioner might choose implementations other than that shownby FIG. 3A. For example, the multipliers 302 and 304 could be replacedwith a table using distributed arithmetic.

FIG. 3B depicts an example embodiment where the circuit 300 includescompute logic 350 to adapt τ, which leads to the funnel filterarrangement discussed above. It should be understood that T computelogic 250 may also be present. The τ compute logic 350 can be configuredto compute a value for τ based on the delayed and undelayed signals fromreceiver (see 228 and 224). Accordingly, as the characteristics of thereceived signal change, the value for τ may adaptively change. Supposewe had a new threshold τ′, and we form the comparator:

$\begin{matrix}{\frac{{{y(k)} - {y\left( {k - L} \right)}}}{\sqrt{{y(k)}^{2} + {y\left( {k - L} \right)}^{2}}} < \tau^{\prime}} & {{Equation}\mspace{20mu}(1)}\end{matrix}$where “y(i)” represents the value of sample i in the signal (where y(k)corresponds to the signal at 224 and y(k−L) corresponds to the delayedsignal 228). This would be an excellent filter, and in fact is equal tothe triple comparator with an adaptive threshold which we now show. Areason as to why this is a good detector is that the top term inside theabsolute value is zero if we have no noise and two valid pulses. If wehave pure noise then the denominator is an estimate of the noisestandard deviation, and hence we have a test which is independent ofnoise variance [constant false alarm rate] and also gives 100% correctdetection, 0% false alarms as the noise vanishes. This latter is calleda consistent test in the statistics literature. Let us square both sidesof the above expression. We obtain, when y(k)>y(k−L), letting

$\frac{y(k)}{y\left( {k - L} \right)} = \omega$after algebra:

${\omega + \frac{1}{\omega}} < \frac{2}{1 - \tau^{\prime}}$Since the left hand side is monotonic 0<ω<1, we can replace τ′ with someother threshold and obtain ω<1 or y(k)<τy(k−L). We conclude that thedetector in equation (1) is equivalent to the detector in FIG. 2D withthe appropriate choice of τ′, i.e. τ=ƒ(τ′). It is intriguing to note wenever need to actually find this function, and furthermore the flow inFIG. 2D is much less expensive computationally than forming the squareroots and ratios and such in equation 1. It should be observed thatequation (1) may, in another embodiment, be modified to include arunning average of past τ to provide a more statistically stableestimate.

In this arrangement, using Equation (1), the compute logic 350 incombination with the comparators 312 and 314 provides a funnel filterbecause the system permits the allowable drift to become wider as thesignal-to-noise ratio (SNR) gets larger. The funnel filter provides atest statistic that allows explicit fast assessment of detection,leakage, and false alarm rates. Through Equation (1) above, the funnelfilter employs τ′, an adaptive value for τ. Thus the pulse collisionfilter depends only on the single threshold T. The motivation is thatthe use of Equation (1) for τ corresponds to allowing a drift of “a”standard deviations while still declaring signal presence. The axesy(k), y(k−L) are shown by 360 in FIG. 3B, and the shaded region in 360is the region where we declare the valid code to be present. A falsealarm occurs when “valid” is declared when the pulse is specious, orsimply noise. This arises when we are inside the shaded region eventhough no valid pulse is present. A detection arises when we are in theshaded region when a signal is indeed present. Being in the shadedregion is unlikely for noise alone because it is unlikely that samples xand y will be close to each other by random chance. The shaded region in360 is verified to have the described funnel form as follows, byreorganizing equation (1): 0<[y(k)²+y(k−L)²]+2y(k)y(k−L)/(τ′−1),τ″=1/(τ′−1) which is a sign indefinite quadratic form associated withthe unitary operator:

$\quad\begin{bmatrix}1 & \tau^{''} \\\tau^{''} & 1\end{bmatrix}$This then defines a funnel as evidenced by properties of conic sections.We only need 360 to determine how to set thresholds, and the circuitsuffices to deliver our decision.

The false alarm rate, P_(fa), required to set the threshold T, is shownin FIG. 3C. The detection probability, P_(d), is used to tune laserpower, or determine achievable range, as well as determining T tobalance P_(d), vs P_(fa). The expression for P_(d), is also shown inFIG. 3C, where Φ is the normal CDF, F the generalized hypergeometricfunction, I the modified Bessel function, δ≡√{square root over (k²+l²)},and λ, λ₊ are the mean signal level and the variance of the receiverrespectively. Finally, the probabilities of a leaker (a falsely declared“own” pulse which is in fact an interfering pulse), P_(leak), is shownby FIG. 3C. These formulations for P_(leak) are approximations; theexact form can be found by deflating the summation limits in the formulafor P_(d). Also note that they are exact only for N_(tuple) equals 2.FIG. 4 shows the (exact) detection performance for a doublet (solid lineonly) and triplet (line-dot) codes. The horizontal axis is the signal tonoise ratio, including both thermal and shot noise, with thermal noisevariance equal to the photon energy. For comparison the false alarm rateis 5×10⁻⁵.

While the specific examples discussed above have involved the use of adelay code where the pulses are transmitted in relatively quicksuccession (and combined to form a pulse return if the decoder indicatesthat the code is in fact valid), it should be understood that longerpulse delays could be employed if desired by a practitioner.

As an example, one can consider a ladar system that is designed to sendout a pulse every 10 μsec. In such a case, a practitioner may use a codewhere the time between codes is a few tens of nanoseconds—for example, 7nanoseconds. In so doing, the system would obtain a new target return,which can take the form of a new point in the ladar point cloud, every10 μsec. The system will have sent two pulses in rapid succession, andit will process the return with a very fast time delay to convert thereturn into a single target return. In other words, the system sendsout, for a pulse doublet scenario, double the number of pulses as thereare points in the point cloud that gets formed.

But, it is also possible to use a delay between 10 μsec shots, andcomparing results shot-to-shot. This has the advantage that the systemproduces one point in the point cloud for each laser shot taken. It alsoallows for more charge time between shots, thereby allows for increasesto the shot energy. For an example where the system could have a lasershot at 0 μsec and then again at 10.007 μsec, and again at 20 μsec and20.007 μsec, etc. The first two shots would then be used as the inputsin FIG. 2A (and subsequent figures). For example, in FIG. 2A, theeven-indexed data returning from time shots at 0 μsec, 20 μsec, 40 μsec,etc. could be fed into the bottom channel 224, and the odd-indexed datareturning from time shots at 10.007 μsec, 20.007 μsec, etc. could be fedinto the top channel 222. It should be understood that for cases wherethe range extent that the ladar system can “see” is less than about 660meters, then the returns from the shot at 0 μsec will die down beforethe shot at 10.007 μsec is launched. This will help avoid ambiguity withrespect to sorting out how to feed the return data into channels 222 and224. This approach also relies on the maintenance of timing accuracyacross pairs of shots, and in this regard, maintaining tens ofnanoseconds of accuracy across tens of microseconds is expected to bewell within the capabilities of currently available timing circuitsgiven that timing circuits with clock drifts of one part in one billionare commercially available, whereas the proposed system here is moremodest at roughly one part in one thousand.

Accordingly, it should be understood that the pulse coding, decoding,and performance modeling discussions herein can be applied to not onlythe short-delay embodiments discussed above but also this long-delayembodiment as well. The design tradeoff for a practitioner will be inchoosing between and balancing laser hardware complexity (forshort-delays) and digital memory (for long-delays).

Delay Code Selection:

Any number of techniques can be used by practitioners to select thedelay codes used by ladar systems in a manner that reduces the risks ofthe same ladar systems in a given area using the same delay codes fortheir ladar pulses.

For example, in several example embodiments, the delay codes can beselected in a non-collaborative/non-cooperative manner where differentladar systems need not have any knowledge of how the other ladar systemsselect delay codes. This can be particularly useful in use casesinvolving vehicles such as automobiles because the reliability oravailability of inter-vehicle communication to collaboratively defineunique delay codes may not be practical. For example, with reference toFIG. 2A, we will want the delays L and M to be distinct so as to avoidpulse collisions where two nearby ladar systems are transmitting encodedladar pulses with the same delays.

FIG. 5 shows an example of how hash codes can be used to generate delaycodes with extremely low likelihoods of pulse collision. At step 500, aprocess generates a random number x that falls within the range between1 and N, where N is the maximum-permitted delay (and where 1 in thisexample is the minimum-permitted delay). This random number can then beselected for the delay L between pulses (step 502). The hardware thatgenerates the random number can be any processor or other circuitrysuitable for such purposes. For example, many of embedded processorsused in automotive industry already have random number generators in thelibrary, which creates a robust set of options for hardwareimplementation. Example hardware for random number generation isavailable from many sources such as NVidia, Xilinx, Altera, etc. WhileFIG. 5 shows delay selection for a doublet embodiment, it should beunderstood that the process flow of FIG. 5 can run multiple times forn-tuple pulse encoding where n is greater than 2. For example, supposewe have N=6 (just like a single die). If we roll a 3, we use a doubletcode spacing of 3. For a triplet code, suppose we roll the dice twiceand get a 4,6. Then our triplet code is three samples spaced by 4 and 6.It can be shown using introductory queuing theory that if two ladarsystems, without any coordinating communication between them, randomlypick their own hash codes, the odds that they accidently choose the samecode is 1 in N². So for N=60 the odds are less than 0.05%. The eleganceof hash codes is that no preparation whatsoever is required. One simplycreates a hash code before any message is sent. That hash code isgenerated with a random number generator. The code can be retained untilsuch a time that the performance is perceived to degrade (examples ofwhich are discussed below), at which point the hash can be updated.Since the code is generated at random, the odds of two ladars choosingthe same code is negligible. With reference to the example embodiment ofthe circuits shown in FIGS. 2A-C and 3A-B, it should be understood thatthe value of the delay imposed by the delay circuits can be adjustableto reflect the chosen hash codes.

Further still, code assignments to ladar systems (such as vehicle codeassignments in an automotive application) can beenvironmentally-dependent. FIGS. 6A and 6B show a scenario fordeveloping a pulse collision performance model. 602 is a performancemetric: D #, the rate of vehicles “blinded” by collision pulse, and 603is another performance metric M #, the rate of vehicles where pulsecollisions arise through multipath. Normally, as shown in FIG. 6A, thedirect path (blinding) arises from pulses in the incoming lane. 629 inFIG. 6B shows the approximate formula for the total number ofcollisions. For example, using the 3^(rd) values in 615,617,618 in thetable of FIG. 6B, and nominal values for other parameters in the table,we obtain 430 pulse collisions per second. Since we chose a demandingcar density, this is conservative. We also assume every vehicle has aladar system. We see that we have 2,400 pulse collisions per second.Thus, 12 bits of isolation suffices even in very dense environments. Wecan achieve this with some optical isolation. If we have 7 bits ofoptical isolation, we would need an additional 5 bits or an effective 32codes in our hash table. One embodiment here would be a 1 ns pulse, dualpulse code spaced up to 0.1 μs apart. This includes a margin forpotential pulse spreading of about 3 ns. In 0.1 μs the two-way time offlight (range resolution) is 15 m. At 50,000 PRF this is also 1/200^(th)of a single range-gated PRF span, so we have ample margin.

In an example embodiment, position detection, such as geographicalposition detection, can be used to adjust and reset the delay codes usedby a ladar system. For example, in a vehicle that is equipped with a GPSor other location-aware system, changes in the vehicle's detectedgeographic position can trigger adjustments/resets of the delay codesused by that vehicle's ladar system. In an example embodiment, the GPSposition can be overlaid with a grid such as a pre-assigned grid ofcellular regions to control delay code adjustments. As a vehicleapproaches a new cellular region (and exits an old cell site), thevehicle's ladar system can be triggered to adjust/reset its delaycode(s) (see FIG. 7 ). Such a design can allow for an efficient re-useof delay codes since a traffic monitoring system can assess offlinevehicle densities as well as line of site blinding conditions (Rm) andconfigure delay code re-use to match the needs of the environment.Importantly, this can be achieved without the need for inter-vehiclecommunications during transit.

In another example embodiment, the signal processing circuit 300 of FIG.3B can be used to extract the delay codes from signals that wererejected by the filter. Delay circuits with varying delays can be usedas additional delay sum circuits to identify the delay codes that may bepresent in rejected interfering signals. This can be performed onrandomized data subsets or it can be done for samples that exceed the Tthreshold set by comparator 234 but fail the tests defined bycomparators 312 and 314. Moreover, this concept can be used with anyn-tuple delay code. The procedure can be:

-   -   1) Count how often the first stage [screening] in FIG. 2D is        triggered,    -   2) Count how often the probing stage rejects the pulse.    -   3) Apply the formulas in FIG. 3C to the results.    -   4) If the false alarms are larger than noise-only dictates, and        the double and triple leaks are high, redo the hash codes,        either in length or delay assignment.

In another example embodiment, vehicle-to-vehicle communication can beused to share codes and collaboratively adjust delay codes to avoidcollisions (see FIG. 8 ).

In yet another example embodiment, the ladar systems can be used tocommunicate in a manner that exploits multipath off of pre-assignedstructures at pre-assigned times. Through such an arrangement, thestructures can be used as billboards to which ladar systems post theirdelay codes. (See FIG. 9 ).

In another example embodiment, the ladar systems can operate tonon-cooperatively (or cooperatively via vehicle-to-vehiclecommunications) generate multi-static fused point clouds. With such anembodiment, pulse interference can be used with appropriate timetransfer for multi-static ladar, thereby presenting detailed volumetricdata from all ladar systems within view.

With a multi-static embodiment, one can assume a ladar system knows (1)the delay codes of all other ladar systems in the area, (2) thelocations of the ladar systems in the area, and (3) the location ofitself, and further assume that the other ladar systems have a clearline of sight to the subject ladar system's receiver. Therefore, if thesubject receiver gets a return from a direct ladar pulse and an echofrom that pulse (e.g., via the road or another car), the larger returnwill be the direct shot. It is expected that all of the shots will beclustered. For example, if Car A's ladar pulse bounces off Car B andthen hits the subject receiver, and if Car A uses two pulses, thesubject receiver will receive 110010 . . . 1001 (where each 1 is a pulse“bang” and each 0 is a non-pulse). The first two pulse bangs in thissequence are strong since they came straight from Car A to the subjectreceiver, and the subsequent pulse bangs will be echoes and henceweaker.

The subject ladar system then creates a pulse code receiver for eachladar system in the area through which it can detect every arrival timeof the pulse doublet (or triplet) from every other ladar system. Foreach doublet (or triplet) pair that is received, the subject system canassociate the largest return as the direct path and the smaller returnwith the echo. The system can then document the time differences betweenthe direct returns and the echoes and combine this with the knowledge ofwhere the subject ladar system is located and where the ladar systemthat sent the pulse bangs is located. This provides partial data onwhere the target producing the echo is located. Multi-static ladar inthis context is a technical term describing the use of multiplevariables in multiple equations to tease out target locations (pointclouds) in this kind of situation.

In another example embodiment, the pulse detections (and any detectionsof interfering pulses) can be used to generate traffic flow informationfor use in traffic monitoring. The ladar-derived traffic information,for example, could be used to augment cellular phone-based crowd-sourcetraffic data to aid traffic routing and the like. This information canbe distributed in real time using vehicle-to-vehicle or other forms ofcommunication. If the vehicle is in a communication-denied area duringpulse collision, then information can be buffered and sent later withscenario-dependent latencies, similar to how cell phone fusion ispracticed. FIG. 6A shows an example, 633/634 of inter vehiclecommunication. If vehicles share point clouds, or track files, during orafter transit, the detail of traffic flow, including the influence ofsignage, or lack thereof, can provide a depth of insight for roadarchitects and transportation planners that is unprecedented. Thus, thesystem can extract “digital exhaust” from pulse collision mitigation andderive system level benefits from these artifacts.

Circuits 220 and 300 can be implemented in any combination ofelectronics, circuitry, hardware, firmware, and/or software that apractitioner would find suitable. However, the inventor further notesthat the elegant simplicity of circuits 220 and 300 allow forimplementation using embedded processor such as a Xilinx Vertex, or Zyncto yield real-time modes of operation. For example, a field programmablegate array (FPGA) can be used to provide the compute resources used bythe circuits 220/300 for processing the samples of the receiver signal.

Furthermore, an FPGA-external SDRAM can be avoided using LVDS ParallelADC, available from Analog devices and other vendors. This reduceslatency and allows the FPGA (or other compute resource such as an ASIC)to dynamically adjust code block length, which can be used for rapidvehicle identifier and block length reassignment. Modern FPGAtransceivers can easily ingest the 6.4 Gigabits per second (Gbps), whichequates to an 8 bit 800 MHz ADC, adequate for a 3 ns laser pulse (forexample).

Furthermore, a FPGA with on-board ping pong memory and cascadeddecimation using multiple DSP cores can provide high performanceimplementation of circuits 220/300. FIG. 10 shows the data flow for thecase of 8 bits, 800 MHz ADC, with a triple pulse code, with maximum codedelay length of 80 nsec. In this example embodiment the triple pulsecode makes use of the pre-add in the Xilinx DSP48E1 core to implementthe sparse delay sum in a single clock cycle in each DSP slice.

In another example embodiment, polarization and/or wavelength diversitycan be used to create the delay code(s) used by a ladar system. Ifdesired, a practitioner could operate with some or all portions ofsparse codes in polarization of wave division space without absorbingtemporal degrees of freedom. For example, consider a doublet code, withdelay D, with a laser capable of operating at twofrequencies/wavelengths F1 and F2. We can have four ladars use the exactsame delay D, but not interfere. This can be accomplished by (1) using,for laser 1, F1 for first pulse and F2 for second pulse, and (2) using,for laser 2, F2 for first pulse and F1 for second pulse, and (3) using,for lasers 3,4, F1 for both pulses and F2 for both pulses respectively.The use of these domains presents the practitioner with options fortrading cost/performance in dense environments.

In other example embodiments, the pulse encoding and deconflictiontechniques described herein can be used with transmitter/receiversystems other than ladar, for example radar systems, acoustic systems,ultrasound systems, or other active navigation aids. A sensor systemwhich involves generating systems for environmental sensing which canpotentially produce troublesome pulse collisions/interference could bebenefited by the techniques described herein.

As a summary, FIG. 11 shows various options for codeassignment/re-assignment in combination with onlinetransmit/receive/detect operations. The code generation transmission andreception is shown above the dotted line. Below the dotted line are thecode assignment and reassignment operations. Codeassignment/reassignment operations that are built and based on theown-car's ladar system (indicated by the laser symbol), and thoserequiring some means of exterior communication (indicated by the Wi-Fisymbol) are so noted in FIG. 11 . It should be understood that the Wi-Ficommunications do not require closed loop real time connectivity. Thedegree of latency tolerated can vary based on applicable circumstances(e.g., to update codes as new vehicles enter the own-car's field of viewversus a need to update factory setting if virtual cells needreconfiguring).

Data Communication:

In another example embodiment, the inventors disclose that the ladarsystem can also be configured to transmit, receive, and/or transceivedata via optical communications. The ability to receive and/or sendinformation other than range point detection data optically via thetechnology disclosed herein can improve the overall situationalawareness for a ladar system (including for a vehicle on which the ladarsystem may be deployed). By using optical communications via the ladarsystem, practitioners can communicate information using a communicationchannel that is already available and (unlike WiFi communications,cellular communications, and/or satellite communications, does notcompete with congested bandwidth on such channels).

However, the use of laser as a means of communication is expected toinvolve relatively consistent laser dosage in certain locations, whichplaces a premium on monitoring and control of laser dosage. Toward thisend, the inventors disclose techniques for laser dosage control withrespect to laser-based data communications. Such dosage control ishelpful for both laser eye safety and avoiding camera damage. Forexample, it has been well-documented that consistent camera exposure atvery short distances (e.g., 2 feet or so) to a laser source that iseye-safe (e.g., class 1) can cause flashing in the camera; and at evencloser ranges (e.g., 6 inches for 10 μJ lasers or 2 inches for 1 μJlasers)—or with a telephoto lens—pixel damage can occur. This is notexpected to be a problem when a ladar system used for optical datacommunication is installed in a vehicle and the vehicle is in motion;but when the vehicle is stopped at intersections, the laser dosage tospecific locations can be expected to be higher (and the presence ofcameras at intersections can also be expected). There are variousapplications which are available for detecting the presence of a camerausing a video imager (see, for example, the “Spy hidden camera Detector”available from Asher L. Poretz in the Apple App Store). Discussed beloware calculations and controls that can be used as part of the system forpurposes of human eye safety as well as camera damage avoidance.

FIG. 12 depicts an example embodiment of an optical receiver 1200 thatcan receive and process not only ladar pulse returns as discussed abovebut also receive and process other optical information. The opticalreceiver 1200 can include a ladar receiver 104 and signal processingcircuit 220 or 300 as discussed above. However, the optical receiver1200 can also include a beam splitter 1202 positioned optically upstreamfrom the ladar receiver 104. The beam splitter 1202 can be configured tocontrollably split incident light 1210 based on the frequency/wavelengthof the incident light. Incident light 1210 that has a frequency orwavelength in a range of frequencies/wavelengths expected for ladarpulse returns 218 can be directed to the ladar receiver 104, andincident light 1210 that has a frequency or wavelength in a range offrequencies/wavelengths not expected for ladar pulse returns 218 can bedirected to the sensor 1204. This allows the beam splitter to re-directlight 1212 to the sensor 1204. Thus, light 1212 can be used as a sourceof information for the optical receiver 1200. Processing logic 1206 canprocess this light 1212 as detected by sensor 1204 to determineinformation about the field of view visible to the ladar receiver 104.The sensor 1204 can be co-bore sited with the ladar receiver 104, whichmeans that the sensor 1204 would be looking at the same scene as theladar receiver 104.

As an example, sensor 1204 can be a camera that receives and processeslight in the visible spectrum. This allows the processing logic 1206 toprocess image data produced by the camera and locate items of interestin the image data. The ability to detect such items can be useful forenhancing the situational awareness of the system in which the opticalreceiver 1200 is deployed (such as a vehicle). For example, theprocessing logic 1206 can use image analysis and object recognition todetect the presence of another vehicle within the image data (or eventhe location of another optical receiver 1200 on the another vehicle).As discussed below in connection with the transceiver embodiment of FIG.13 , messages could then be targeted at this detected vehicle using thetargeting capabilities of ladar transmitter 102.

Message information can be encoded in laser pulses using delays, and thereceiver can measure these delays as part of the processing in FIG. 2C.If the pulse delay is not the code used by the host laser, then thepulse pair can be rejected. Through the use of a communication protocolsuch as header message formats, the receiver will be able to know that amessage is being sent. As an example, suppose the source laser uses adelay of “a” seconds for sending a “0” bit and a delay of “b” secondsfor sending a “1” bit. Then, the source laser can send a group of pulsesall with the delay “a”, then another group of pulses all with delay “b”.The receiver then observes a repeat transmission which tells it thatthere is a code from a single source laser because a plurality of sourcelasers sending messages would not provide repeat transmissions. Hence,the receiver knows that (i) another system is trying to communicate, and(ii) the communication code is being shared through redundancy. Oncesufficient repeats have been sent out, the sending laser can now sendinformation using the code book [e.g., “a” delays for “0”, “b” delaysfor “1”] that the receiver now possesses.

A benefit of bore siting the camera with the ladar receiver 104 is thatthis avoids disruptive parallax (at least on the receive side) betweenthe active laser and passive optics, which allows for precise control ofa targeted laser. While of value for forming laser point clouds, thisprecision of control is also of great practical value in using the ladartransmitter 102 as a communication source because it allows the passivevideo optics to find the exact location of the other vehicle's receiver(and then quickly transmit data at that location by firing its laser). Asecond video camera can also be used, with the stereo vision providingadditional localization acuity.

To further reduce the risk of node-to-node interference, a telescopinglens can be included in a transmit path for the system (see 1350 in FIG.13 ). The telescoping lens 1350 permits the system to target light onthe intended optical collector, even over larger distances, by adjustingthe beam divergence to match the size of the receiver's photodetector.

FIG. 13 shows an example optical transceiver 1300 that employs a ladartransmitter 102 and ladar receiver 104, and is capable of receivinginformation optically as discussed above in connection with FIG. 12 .The transceiver 1300 includes a sensor 1302 that is positioned to senseand pass light 1310 sent by the ladar transmitter 102. This light 1310may comprise ladar pulses 110 as discussed above, but it could alsocomprise other forms of light that are meant to convey informationoptically, such as a probing message or the like.

In an environment where multiple optical transceivers 1300 are deployedon multiple vehicles that are within the vicinity of each other, theoptical transceivers 1300 can leverage the data communication techniquesdescribed herein to achieve targeted point-to-point communicationsbetween specific vehicles. The targeted point-to-point nature of thiscommunication can be understood when considering that the size of anexample laser with a nominal beam divergence of 3 mrad is only about 6inches in diameter at 50 m. Therefore, the optical transceiver 1300 canbe configured to selectively illuminate relatively small areas withinwhich a targeted optical receiver is located. This can be contrastedwith communications over a cellular network where every receiver withina network cell will be bathed in radiofrequency energy.

Heat Map Analysis and Control:

Sensor 1302 can help the transceiver 1300 maintain eye safety duringoptical transmissions. For example, to maintain connectivity in a freespace link when the transmitter is used in a free space, point-to-pointoptical data communication system, there is a possibility that a heavydosage of light will be directed at a specific location. If leftunchecked, this could pose eye safety concerns. Moreover, such riskcould be heightened in example embodiments where a telescoping lens 1350is employed because the telescoping lens 1350 can reduce beam divergencewhich therefore might increase the energy that could enter the pupil ofa person who happened to be positioned in the line of sight between theoptical transmitter and the optical receiver. This use as a free space,point-to-point optical data communication system stands in contrast touse as a scanning ladar transmitter where the laser light is expected toconstantly scan which will dilute the optical dose at any fixedlocation. Thus, the sensor 1302 can help maintain eye safety by workingin concert with control system 106 by maintaining a heat map or runningtally of the last dosage delivered to locations within the field ofview.

FIG. 14A illustrates an example of how a heat map control process can beimplemented. The control process can begin with an initialization of theheat map. The heat map can have rows and columns that correspond to theachievable azimuth and elevation laser shot locations. This heat map canbe accessible to the scheduler for the ladar transmitter. At initiation,the system can set the heat map to zero, and it can also set the maximumallowed dosage (md). The value for md in an example can be setarbitrarily at 20 units. The control process then loops through allscheduled shots. As an example, laser shots may arise on the order ofmicroseconds spacing, so a queue depth of hundreds of shots may be usedto help avoid race conditions while presenting minimal latency impact.

At time K, the system inspects the next scheduled shot, and the systemalso inspects the current heat map as well as the energy planned for thenext scheduled shot. In the running example, at time K, the associatedKth scheduled shot will be fired at row 2, column 1, with a scheduledshot energy of 8 units of energy. The system can then compute the nextheat map entry at the heat map element corresponding to row 2, column 1as 10+8=18. This is less than the maximum dosage (md) of 20 units, sothe system can take the scheduled laser shot. If instead the scheduledshot energy was 11 units, this means that the system would need to delaythe shot or reduce the shot energy.

As additional comments on the heat map control features, the inventorsnote that the azimuth and beam locations in this example embodiment arenot corresponding to fixed physical locations when the vehicle ismoving. Further they do not correspond to the time varying position ofeye position for moving observers. Currently international laser eyesafety regulations do not address the problem of accounting for bothown-car motion as well as that of other observers or vehicles inconstructing dosage models. However, anticipating evolutions in lasereye safety standards as technology evolves and markets expand, theinventors posit that such additions might be desired and can beimplemented using techniques described herein. The current eye safetystandards specify a distance of 10 cm for 10 mW, and at such ranges therelative motion between observer and laser is a moot point. To implementobserver relative motion, for moving vehicle and fixed observers, thesystem could use a map, and convert azimuth and elevation to maplocations.

The inventors further note that the heat map matrix is expected to begenerally large, for example an array of over 10,000 entries. However,this is well within the scope of many existing commercially availableprocessors for maintaining real time heat map management and control.

Also, while the maximum dosage (md) used in the example discussed aboveis a static value, it should be understood that the system could employa variable maximum dosage. For example, the maximum dosage can beadjusted for the presence of a camera. Given that it is expected thatthe camera will need to be very close to the laser for the laser topresent a hazard to the camera, this may be a risk that is largelyconfined to dense urban environments while a vehicle is parked.

The control system 106 can use the heat map to constrain the shot listused by the ladar transmitter 102 when firing the laser. If a particulardestination location is getting too close to being overly dosed withlight as determined from the heat map, the shot list delivered to theladar transmitter 102 can be adjusted to remove shots that would targetthat particular destination location for a specified window of time (orreduce the shot energy if possible). For example, it may be desirable toensure that no more than 10 mW of laser light enters a human pupil overa 1 second interval. This means that a 1 W laser can likely only operateas a free space optical communication transmitter to a targetedreception location over a 1 sec interval using 1% of net energy (since10 mW is 1% of 1 W).

Thus, the optical transceiver 1300 can operate in both a ladar mode anda free space optical communication mode. When operating in the ladarmode, the transceiver 1300 can transmit and receive ladar pulses asdiscussed above to determine range information for objects within thesystem's field of view. When operating in the free space opticalcommunication mode, the transceiver 1300 can receive optical informationvia the path through the beam splitter 1202 and sensor 1204, and thetransceiver can also send optical information via the ladar transmitter102 (or other light source if desired).

Control system 106 can translate range points into a shot list asdescribed in the above-referenced and incorporated patent applications,and the ladar transmitter 102 can use this shot list to target ladarpulses using a beam scanner and compressive sensing as described in theabove-referenced and incorporated patent applications. The ladartransmitter 102 can either share the same lens as the ladar receiver 104(in which case polarized light can be used) or be located in proximityof the ladar receiver 104.

Light 1320 is light from another ladar system that, like the lasersource 1310 from the ladar system in FIG. 13 encompassed by the box1300, is incident on optical detector 1304. This light is commingledwith light 1310 and both are passed to the beam splitter 1202 (see light1210), which in turn re-directs this light to the sensor 1204 if thelight 1210 exhibits a frequency meant to be used for opticalcommunications. Data such as image data from sensor 1204 can be passedto the control system 106 via data link 1312, and the processing logic1206 discussed above in connection with FIG. 12 can be embedded into thecontrol system 106. Thus, control system 106 can process the informationon link 1312 to locate objects of interest in the transceiver's field ofview such as an optical receiver on a vehicle or other object (e.g., afixed item of infrastructure such as a traffic sign, cell tower, etc.).The control system 106 can also determine a location for the object ofinterest, such as the azimuth and elevation orientation of the object ofinterest. If the control system 106 decides that the object of interestshould be targeted with a ladar pulse 110 or an optical message of somesort, it can insert a range point into the shot list that is targeted tothe determined location of the object of interest.

Meanwhile, sensor 1302 can be sensing and tracking the amount oftransmitted light 1310, and this dosage information can be fed back tothe control system 106 via data link 1316 so that the control system 106can maintain and update the heat map which tracks light dosage perlocation over time. Given that the control system 106 can know where theladar transmitter 102 is targeted at any given time, this informationcan be correlated with the sensed dosage information in link 1316 tobuild and update the heat map. The control system 106 can then use thisheat map to modify the shot list (and/or reduce shot energy) as neededto prevent a particular location from being dosed with too much lightover a specified window. Thus, the heat map can be used to decidewhether a scheduled shot from the shot list should be canceled,re-scheduled, and/or have its shot energy reduced. In FIG. 14A, nowindow is shown; but the system can convert a constantly growing heatmap with a running average by subtracting older data from the heat map.This can be done by replacing the update step for the heat map from FIG.14A with a new update scheme as shown by FIG. 14B, where m is theduration of the running window.

Furthermore, the system can also exercise control to selectively avoidfiring laser shots at specific locations. These specific locations canbe referred to as “keep away” locations. With reference to FIGS. 12 and13 , the sensor 1204 and processing logic 1206 can cooperate to identifyelements in the environmental scene that correspond to designatedobjects that a practitioner wants to avoid dosing with laser light. Forexample, processing can be performed on data produced by sensor 1204 toidentify objects such as cameras, human faces, strong retro-reflectors,other ladar receivers not disclosed from cross-communication, and freespace optical nodes. Image processing and pattern matchingclassification techniques can be used to detect such objects ofinterest. Upon identifying such objects and determining their locations(e.g., azimuth and elevation locations) in the environmental scene,these locations can be designated as “keep away” locations in the heatmap. In this fashion, if the system encounters a shot on the shot listthat is targeted to such a “keep away” location, the system can thenconsult the heat map to conclude that such a location should not betargeted with a ladar pulse and adjust the shot list accordingly. Theheat map can indicate such “keep away” locations via any of a number oftechniques. For example, the “keep away” locations can have their heatmap data values adjusted to match or exceed the maximum dosage, in whichcase the system will avoid firing laser shots at such locations. Asanother example, the heat map data structure can include a separate flagfor each indexed location to identify whether that location is a “keepaway” location. As yet another example, the heat map data structure cancomprise two independent data structures, one that tracks dosage overtime for the various locations and one that identifies keep awaylocations over time.

An optical transceiver 1300 can thus communicate bidirectionally overfree space 1320 to not only perform range point detection andmeasurement but also communicate data optically. As an example, suchdata communications can used by vehicles to share delay codes to reducethe potential for interference within a given environment. However, itshould be understood that other information could be shared as well,such as traffic data, ladar point clouds, text messages, etc., with theimagination of a practitioner and tolerable latency being the onlyconstraints.

While the invention has been described above in relation to its exampleembodiments, various modifications may be made thereto that still fallwithin the invention's scope. Such modifications to the invention willbe recognizable upon review of the teachings herein.

What is claimed is:
 1. An apparatus comprising: a ladar receivercomprising: a photodetector that senses incoming light and generates asignal representative of the sensed incoming light, wherein the incominglight comprises a combination of an own pulse reflection and noise,wherein the own pulse reflection comprises a plurality of pulsesseparated by a known delay; and a signal processing circuit that (1)computes a delay sum signal based on the generated signal and the knowndelay and (2) detects the own pulse reflection within the generatedsignal, wherein the signal processing circuit detects the own pulsereflection based on: a comparison of the delay sum signal with a firstthreshold; a comparison that determines whether the generated signal isless than the delay sum signal multiplied by a second threshold; and acomparison that determines whether the delay sum signal is less than thegenerated signal multiplied by the second threshold.
 2. The apparatus ofclaim 1 wherein the delay sum signal is based on a doublet pulseseparated by the known delay.
 3. The apparatus of claim 1 wherein theknown delay comprises a first delay and a second delay, wherein thedelay sum signal is based on a triplet pulse, wherein a first pulse anda second pulse of the triplet pulse are separated by the first delay,and wherein the second pulse and a third pulse of the triplet pulse areseparated by the second delay.
 4. The apparatus of claim 3 wherein thefirst and second delays are different values.
 5. The apparatus of claim1 wherein the known delay comprises a plurality of N−1 delays, andwherein the delay sum signal is based on an N-tuple pulse, wherein the Npulses are separated respectively by the N−1 delays.
 6. The apparatus ofclaim 1 wherein the second threshold is a value greater than
 1. 7. Theapparatus of claim 1 wherein the first and second thresholds areadjustable.
 8. The apparatus of claim 1 wherein the known delay isadjustable.
 9. A ladar method comprising: sensing incoming light,wherein the incoming light comprises a combination of an own pulsereflection and noise, wherein the own pulse reflection comprises aplurality of pulses separated by a known delay; generating a signalrepresentative of the sensed incoming light; computing a delay sumsignal based on the generated signal and the known delay; and detectingthe own pulse reflection within the generated signal based on (1) acomparison of the delay sum signal with a first threshold, (2) acomparison that determines whether the generated signal is less than thedelay sum signal multiplied by a second threshold, and (3) a comparisonthat determines whether the delay sum signal is less than the generatedsignal multiplied by the second threshold.
 10. The method of claim 9wherein the delay sum signal is based on a doublet pulse separated bythe known delay.
 11. The method of claim 9 wherein the known delaycomprises a first delay and a second delay, wherein the delay sum signalis based on a triplet pulse, wherein a first pulse and a second pulse ofthe triplet pulse are separated by the first delay, and wherein thesecond pulse and a third pulse of the triplet pulse are separated by thesecond delay.
 12. The method of claim 11 wherein the first and seconddelays are different values.
 13. The method of claim 9 wherein the knowndelay comprises a plurality of N−1 delays, and wherein the delay sumsignal is based on an N-tuple pulse, wherein the N pulses are separatedrespectively by the N−1 delays.
 14. The method of claim 9 wherein thesecond threshold is a value greater than
 1. 15. The method of claim 9further comprising: adjusting the first threshold and/or the secondthreshold.
 16. The method of claim 9 further comprising: adjusting theknown delay.
 17. An apparatus comprising: a ladar transmitter comprisinga plurality of scannable mirrors, wherein the ladar transmittertransmits a plurality of ladar pulses toward a plurality of targets in afield of view via the scannable mirrors, wherein the ladar transmitteris operable to switch between transmitting the ladar pulses via thescannable mirrors in a ladar mode and an optical communication mode,wherein the ladar pulses encode data messages when the ladar transmitteris operating in the optical communication mode; a ladar receiver thatreceives and processes reflections of the ladar pulses transmitted bythe ladar transmitter when operating in the ladar mode to perform rangepoint measurements with respect to targets that were targeted by theladar transmitter when operating in the ladar mode; a memory for storinga data structure that tracks laser dosages delivered by the ladartransmitter to a plurality of different locations in the field of viewover time; and a processor that controls the ladar transmitter whenoperating in the ladar mode and when operating in the opticalcommunication mode based on the tracked laser dosages from the datastructure.
 18. The apparatus of claim 17 wherein the data structurecomprises a heat map data structure that tracks the laser dosages forthe locations in the field of view over a defined time window, whereinthe heat map data structure comprises a plurality of data values indexedby azimuth and elevation locations, and wherein the data valuesrepresent the tracked laser dosage for the indexed azimuth and elevationlocations.
 19. The apparatus of claim 17 wherein the processor schedulesa plurality of the ladar pulses based on the tracked laser dosages fromthe data structure.
 20. The apparatus of claim 17 wherein the processorcontrols the ladar transmitter based on the tracked laser dosages fromthe data structure to avoid transmitting a ladar pulse to a location inthe field of view that would cause the tracked laser dosage for thatlocation to exceed a defined threshold.
 21. The apparatus of claim 17wherein the ladar pulses used for the optical communication mode exhibita different frequency or wavelength than a frequency or wavelengthexhibited by the ladar pulses used for the ladar mode.
 22. The apparatusof claim 21 wherein the apparatus is arranged as an optical transceiver,the optical transceiver further comprising: a beam splitter; and asensor; wherein the beam splitter (1) directs incident light thatexhibits a frequency or wavelength corresponding to the frequency orwavelength for the ladar mode to the ladar receiver and (2) directsincident light that exhibits a frequency or wavelength corresponding tothe frequency or wavelength for the optical data communication mode tothe sensor; and wherein the sensor and the processor cooperate to detectand extract data from an incoming optical data signal.
 23. The apparatusof claim 21 wherein the processor (1) determines a location in the fieldof view where a device is located that is capable of receiving the datamessages and (2) identifies the determined location as a target for oneor more ladar pulses in the optical communication mode that encode oneor more data messages to be communicated to the device.